LExEn: Hyperthermophiles of the Hydrothermal Vent Subsurface and Their Environmental Tolerance

从深海热液喷口分离出来的嗜热古细菌在极端高温、高压和极有可能的化学毒性下生存和生长。在热液喷口流出物和海底火山喷发的固体中对它们的分离和检测强烈表明，它们也存在于高温和缺氧的地下环境中。它们在极端的地下热液喷口条件下（pH值、硫化物、金属、温度和压力）生存或生长的能力将表明这些生物是否有潜力成为广泛存在和环境耐受的地下深处居民。除了温度和一定程度上的压力外，许多决定喷口超嗜热微生物在地下条件下生长和存活的关键因素尚未经过测试，这阻碍了对这些生物的发生范围和环境耐受性的现实评估。该项目将测试热液喷口古细菌实际上生长在热、厌氧和有毒的热液喷口地下的假设，最有可能沿着喷口流体穿过多孔或洞穴状岩石的流动路径生长。这些实验将使用四种热液喷口超嗜热古细菌，即产甲烷菌jannaschii产甲烷球菌、异养硫还原剂烟性热球菌、热球菌属菌株GB-D和硫酸盐还原剂深生古球菌。这些古细菌被选为厌氧、嗜热代谢的横截面，它们是热液喷口古细菌种群的代表，具有承受地下条件的生理潜力。最重要的是，这些属是直接从正在进行的海底喷发和喷口巨羽流中分离出来的。我们将系统地测试这些古细菌在近似的原位条件下的生长和生存：大洋中脊热液喷口及其地下延伸的高静水压力；酸性pH值;高硫化物和金属浓度。这些因素将分别测试，并以接近自然情况的方式一起测试。通过单因素实验和多因素实验的对比，验证了这些应激因素对热液喷口古菌在地下环境中生长和存活的协同效应与单个因素的影响有较大差异的假设。影响生长和生存的一个重要特征是生物膜的形成，直到最近才对古细菌模型系统进行了研究。由于生物膜的形成增强了许多细菌的环境耐受性，热液喷口和地下环境中的古细菌生物膜可能对环境胁迫因素表现出更高的耐受性。换句话说，热液喷口和地球地下生物圈中最具抵抗力的生物可能不是古细菌，而是古细菌生物膜。这些实验的目的是综合几种物理和化学因素，这些因素共同决定了地球上一些最极端的生命形式的容忍极限。

LExEn: Hyperthermophiles of the Hydrothermal Vent Subsurface and Their Environmental ToleranceHyperthermophilic archaea, isolated from deep-sea hydrothermal vents, survive and grow under extreme heat, pressure, and most likely chemical toxicity. Their isolation and detection in hydrothermal vent effluents and in solids from undersea volcanic eruptions strongly suggest that they also occur in hot and anoxic subsurface environments. Their ability to survive or grow under extreme subsurface hydrothermal vent conditions (pH, sulfide, metals, temperature, and pressure) will show whether these organisms have potential as widespread and environmentally tolerant deep-subsurface inhabitants. With the exception of temperature, and to some degree pressure, many critical factors which determine growth and survival of vent hyperthermophiles under subsurface conditions have not been tested, preventing a realistic assessment of the occurrence range and environmental tolerance of these organisms.This project will test the hypothesis that hydrothermal vent archaea actually grow inthe hot, anaerobic and toxic hydrothermal vent subsurface, most likely along the flow paths of vent fluids through the porous or cavernous rock. Four hydrothermal vent hyperthermophilic archaea will be used for these experiments, the methanogen Methanococcus jannaschii, the heterotrophic sulfur reducers Thermococcus fumicolans, Pyrococcus sp. strain GB-D, and the sulfate reducer Archaeoglobus profundus. These archaea were selected as a cross-section of anaerobic, thermophilic metabolisms which are representative for hydrothermal vent archaeal populations, and have the physiological potential to withstand subsurface conditions. Most importantly, these genera have been isolated directly from ongoing undersea eruptions and vent megaplumes. We will systematically test the growth and the survival of these vent archaea under approximated in situ conditions: high hydrostatic pressure of mid-ocean ridge hydrothermal vents and their subsurface extensions; acidic pH; and high sulfide and metal concentrations. These factors will be tested individually, and together in ways that approximate the natural situation. The hypothesis that the synergistic effects of these stress factors on growth and survival of hydrothermal vent archaea in the subsurface environment will differ considerably from the effect of each factor alone will be tested by comparing single-factor and multi-factor experiments. An important feature which influences growth and survival is biofilm formation, only recently studied for archaea model systems. Since biofilm formation enhances the environmental tolerance of many bacteria, archaeal biofilms in hydrothermal vent and subsurface environments are likely to show increased tolerance to environmental stress factors. In other words, the most resistant organism of hydrothermal vents and the earth's subsurface biosphere may not be an archaeon, but an archaeal biofilm. These experiments aim at integrating several physical and chemical factors which together determine the tolerance limits of some of the most extreme life forms on earth.